I had sex with my husband around July 16-19. My last period was June 27-July 1 which is my normal 5 day cycle. I had some bleeding/spotting start on July 25 and only last 3 days and was much lighter than normal. At first I thought it was my period but thought it was weird that it only lasted 3 days. Then I heard about implantation bleeding. Since then I have taken a test each week and they all come up negative. I'm not sure if its too early to tell or if I am being too paranoid.